Process of forming a matrix structure



Feb. 11, m

PROCESS OF FORMING A MATRIX STRUCTURE Original Filed Oct. 1, 1963 INVENTOR. 05cm A. DRAKE ATTORNEY o. A. DRAKE 3,427,644

United States Patent 3,427,644 PROCESS OF FORMING A MATRIX STRUCTURE Oscar A. Drake, Fort Wayne, Ind., assignor to Sylvania Electric Products Inc., a corporation of Delaware Original application Oct. 1, 1963, Ser. No. 312,903, now Patent No. 3,305,743, dated Feb. 21, 1967. Divided and this application Nov. 23, 1966, Ser. No. 596,569 U.S. Cl. 51319 7 Claims Int. Cl. B24c 1/04, 1/06, 3/32 ABSTRACT OF THE DISCLOSURE The process for treating the interior and exterior surfaces of the matrix of an electrostatic printing cathode ray tube wherein pressurize-d blasts of abrasive material are directed against the respective matrix surfaces at a substantially perpendicular relationship thereto. The blasts and matrix are moved relative to one another'in a lateral manner at a controlled rate to clean and abrade the exposed portions of the conductive elements and the interstitial areas therebetween.

This invention relates to electrostatic printing cathode ray tubes in general and more particularly to a method for achieving an improved matrix structure for electrostatic printing'tubes. The present invention is a division of an application having Ser. No. 312,903 filed Oct. 1, 1963, now Patent No. 3,305,743, dated Feb. 21, 1967, and assigned to the same assignee as the subject application.

Electrostatic printing cathode ray tubes are well known devices having found use in many rapid printing applications such as address label printing and facsimile transmission of intelligence.

A typical printing tube is constructed of a glass envelope containing an electron beam generating source at one end and a printing matrix array hermetically sealed or bonded to the opposite end. The printing matrix compries a discrete array of a plurality of microminiature electrical conductors sealed parallel in spaced relationship to each other in a substrate of insulative material with the conductors extending interiorly to exteriorly therethrough. Typically such conductors may be tungsten wires having diameters of 0.001 inch sealed in a borosilicate glass on centers of 0.004 inch thereby giving a density of 62,500 conductors per square inch.

A printing tube of this nature is conventionally operated at relatively high voltages, as for example, minus 18 kilovolts cathode voltage with reference to zero anode voltage and small electron beam currents. A regulated electron beam emanating from the electron beam or gun source within the tube is caused to scan the interior surface of the matrix so as to impart a small electron beam current to selected conductor elements in the matrix array. Present arrays require a 300-400 volt conductor element buildup, acquired from the electron beam, to impart a sufiicient electrostatic negative charge for printing purposes. A moving paper belt having a coating thereon receptive to electrostatic charge deposition, is drawn across the exterior surface of the matrix, thereby acquiring a latent image composed of negative electrostatic charge patterns from the conductor elements. Subsequent processing of the latent image on the paper belt produces a printed copy of the electrically transmitted information.

In some cases electrostatic printing tubes have exhibited serious flaws or defects such as areas of dead or no copy, and areas of skip or intermittent copy. Dead copy manifests itself as completely non-printing areas of the matrix and is caused by undesirable insulative films of glass or metallic oxide over the matrix conductor elements. Skip copy manifests itself as intermittent printelectron 3,427,644 Patented Feb. 11, 1969 ing areas of the matrix and is caused by arcing and leakage between the conductors of the matrix array. Yet another prevalent type of defect is that of conductor elements snagging or abrading the moving paper belt as it passes over the exterior surface of the printing matrix.

Attempts have been made to remove the undesirable insulative films, burrs, and contaminants by chemical cleaning. These attempts have proven unsatisfactory as chemical cleaning is selective and will remove only those materials which are affected by the particular chemical in use.

Accordingly, an object of this invention is to provide an improved electrostatic printing tube which does not exhibit dead areas of copy resulting from insulative films over the conductor elements.

Another object of this invention is to provide an improved electrostatic printing tube which does not exhibit skip areas of copy resulting from arcing and leakage between conductor elements.

Yet another object of this invention is to provide an improved electrostatic printing tube having a printing matrix surface which does not abrade the coated paper belt moved contiguously thereover.

The foregoing objects are achieved in one aspect of the invention by providing an improved matrix structure for an electrostatic printing tube and through the use of a processing procedure wherein a pressurized blast of abrasive material is directed against the surfaces of the printing matrix to clean and 'de-lburr the conductor elements, and abrade and roughen the matrix glass surfaces.

For a better understanding of the present invention together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a typical electrostatic printing cathode ray tube;

FIG. 2 is an enlarged cross-sectional view of a typical printing matrix;

FIG. 3 is a view showing the abrasive processing of the printing tube matrix; and

FIG. 4 is an enlarged cross-sectional view of a printing matrix after abrasive processing.

For a better understanding of the invention there is shown in 'FIG. 1 a typical electrostatic printing cathode ray tube 11 comprising an envelope 13 containing an beam source or gun 15 from which issues an electron beam 17 directed to impinge on the printing matrix 19 which is integrally bonded to the envelope. The paper belt 21, coated to be receptive to electrostatic charge deposition, is caused to moved over the matrix 19 during operation in a prescribed manner by means not shown.

In greater detail FIG. 2 illustrates the construction of a typical printing matrix 19 wherein the electrically conductive element 25 having diameters of 0.001 inch are hermetically sealed on centers of 0.004 inc-h in an insulative material 27 to extend interiorly to exteriorly therethrough to form parallel arrays having insulating interstitial spaces 29 separating them one from the other. The conductor elements 25 are preferably selected from the group of refractory metals including such representative metals as tungsten, molybdenum, tantalum, rhenium, hafnium, and niobium.

The insulative material 27 used to seal the conductor elements 25 is a ceramic material chosen to facilitate the formation of an optimum bond with the metal selected for the conductor elements and at the same time exhibit the desired electrical properties especially relating to resistivity and dielectric constant. Suitable ceramic materials 27 to form such an optimum bond with the above stated refractory metals can be found in glasses having a dielectric constant of less than 7.0 of which the borosilicate family of glasses is an example.

The interior interstitial surface 30 and the exterior interstitial surface 31 of the matrix 19 are initially relatively smooth, and since there are interstitial spacings of only 0.003 inch separating adjacent conductors 25 these surface areas need to be made free of all contamination or bulb manufacturing residues. Many of the conductor elements 25 are apt to have protruding burrs 33 on the ends thereof. In addition these conductor elements may be coated with an undesirable insulative film 35 of glass or oxide residue from the bulb manufacturing operation. It is quite evident that if the burrs 33 are not removed they are apt to abrade the coated paper belt 21 as it passes over the matrix 19. Further the burrs reduce the surface interstitial spacing or area between adjacent conductors 25 whereby arcing or leakage is promoted therebetween. The aggravating insulative films 35 cause continuity malfunctions which result in dead areas of printed copy on the treated paper belt.

Processing of the printing tube matrix is shown in FIG. 3. The interior pressurized blast nozzle 39 being inserted into the envelope 13 is positioned to direct the interior abrasive pressurized blast 41 issuing from the nozzle 39 to impinge on the interior interstitial surface 30. An exterior nozzle 40 is used to direct the exterior abrasive pressurized blast 42 to impinge on the exterior interstitial surface 31. The nozzles 39 and 40 are positioned at substantially right angles to the matrix 19 to insure most effective abrading. In operation, the matrix 19 and the nozzles 39 and 40 are caused to experience a controlled lateral relative motion such that the abrasive blasts 41 and 42 will uniformly clean and abrade the matrix surfaces 30 and 31. The a'brasion operational conditions concerning pressure, duration of abrasion, and rate of relative motion are mutually dependent such that no one pressure, time, or rate can be specified as optimum independently of the others.

As shown in FIG. 4 the pressurized abrasive blast abrades the terminal portions of conductor elements 25 so that they are free of lburrs and with essentially rounded exterior terminal portions 51 extending one half to two conductor element diameters beyond the roughened exterior interstitial surface 53. Experience has demonstrated that the rounded terminal portions 51 extending one half to two element diameters beyond the exterior surface 53 are sufiiciently protruding to effectively contact the moving paper belt 21 to impart thereon the desired electrostatic charges, but as such are not overly protruding so as to impede the travel of the belt 21 as it moves over the exterior surface 53. The roughened surface 53 provides a clean and lengthened leakage path between adjacent conductive elements 25. The removal of burrs 33 from the terminal portions of the conductive elements reduces arcing between adjacent elements and also eliminates destructive abrasion of the coated paper belt 21 as it passes over the exterior terminal portions 51 of conductor elements 25. The interior terminal portions 57 of conductors 25 are also cleaned of burrs 33 and films of insulative materials 35 which inhibit the reception of current from the electron beam. The interior terminal portions 57 of the conductor elements 25 are abraded so as to be substantially rounded and essentially flush with the roughened interior interstitial surface 55 which is cleaned and roughened to enhance insulative capabilities between adjacent conductors 25. Terminal portions 57 are cleaned of contamination and films of ceramic and metallic oxides so as to make the conductors 25 ready receptors of current from the electron beam 17.

The abrasives used in this abrading process should preferably be electrically nonconductive and have a minimum hardness rating of at least 5.5 on Mohs scale of scratch hardness. This degree of minimum hardness is specified to provide particles which will effectively abrade the insulative materials 27 normally used, such as borosilicate glasses having a range of 5.0-5.5 on Mohs scale of scratch hardness. Also the refractory metals forming conductive elements 25, which have more abrasion resistance than the aforementioned glass, must be sufiiciently abraded by particles of a given hardness to adequately clean and remove burrs 33 as required of this process. The nominal particle size is less than the 0.003 inch spacing between adjacent conductor elements 25 to permit the particles to facilely enter therebetween and achieve the desired abrasion and cleaning of the interstitial surfaces 53 and 55 and the conductor element terminal portions 51 and 57. Examples of satisfactory abrasive materials, though not restricted to such, are aluminum oxide, silicon carbide, cerium oxide, and boron nitride. While a dry abrasive is preferred, a Wet slurry type abrasive may'be used with success. After the abrasion operation, the envelope 13 is cleaned in preparation for subsequent manufacturing operations.

Thus, there is provided an electrostatic printing tube having an improved printing matrix that eliminates dead or skip areas of copy. The roughened surfaces of the improved matrix provide increased insulation areas between adjacent round-ended conductive elements to effect a drastic reduction in leakage and arcing therebetween.

The abrasive processing removes inherent burrs from the terminal portions of the conductors, eradicates undesirable insulative and conductive surface contaminants, roughens the interstitial surface, and provides substantially rounded tenminal portions on the conductive elements thereby assuring improved printing efficiency and reliability. These factors result in a printing matrix that exhibits a degree of superior performance heretofore unattained.

While there has been shown and described what is at present considered the preferred embodiment of the invention it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. A method for treat-ing an electron target printing matrix of an electrostatic printing cathode ray tube, said matrix being formed of a substrate of insulative material having therein a plurality of spaced electrically conductive elements of refractory metal of substantially like diameters and exhibiting :a greater abrasion resistance than that of the substrate, the elements being insulated by interstitial areas of said insulative material and oriented to extend interiorly to exteriorly therethrough in a manner to provide exposed terminal portions on the interior and exterior surfaces thereof, said method comprising the steps of:

directing pressurized blasts of abrasive electrically nonconductive material against the respective interior and exterior surfaces of said matrix in substantially right angle relationship thereto to insure effective abrading; and

moving said blasts and said matrix relative to one another in a substantially latenal manner at a controlled rate to uniformly cover said terminal portions of said conductive elements and said interstitial areas of said matrix to produce a degree of abrasion to provide cleaning and de-burring of the ends and exposed portions of said elements and to effect cleaning and abrading of said interstitial areas to enhance the insulative properties thereof; said exterior surface of said matrix being abraded to a greater degree than the interior surface thereof to provide the protrusion of said exterior terminal portions therefrom.

2. The method according to claim 1 wherein said abrasive material has a maximum particle size which is less than said spacing between said conductive elements.

3. The method according to claim 1 wherein said abrasive material has a minimum hardness rating in the range of 5.0-5.5 on Mohs scale of scratch hardness.

4. The method according to claim 1 wherein said abrasive material is a dry substance.

5. The method according to claim 1 wherein said abrasive material is a slurry conveyed substance.

6. The method according to claim 1 wherein the abrasive blasting of said interior matrix surface is of a degree to tabr-ade the interior terminal portions of said conductive elements to effect substantially rounded ends thereon that are substantially flush with the roughened interior interstitial surface of said matrix.

7. The method according to claim 1 wherein the abrasive blasting of said exterior matrix surface is of a degree to abrade the exterior terminal portions of said conductive elements :and said surrounding interstitial surface areas in .a manner that said terminal portions have substantially rounded ends and extend one-half to two conductive element diameters beyond the roughened exterior interstitial surface of said matrix.

References Cited UNITED STATES PATENTS 2,189,985 2/1940 Hickok 51-319 X 2,200,587 5/1940 Tirrell 518 2,650,191 8/1953 Teal 313-329 X 2,710,286 6/1955 Zachariason 51 320 X 2,758,423 8/1956 Lande 51 11 2,984,535 5/1961 Traite 61 211 313 73 X 3,040,124 6/1962 Camras 313-73 x FOREIGN PATENTS 659,176 3/1963 Canada.

LESTER M. SWINGLE, Primary Examiner. 

